1. Field of Invention
The present invention is generally related to levels that include level vials and the manufacturing of such level vials.
2. Description of Related Art
Horizontal level indicating vials that are mounted on levels have traditionally been square or rectangular. Level vials are manufactured by first extruding or injection molding a blank. Extruded blanks are cut to length, and an internal cavity is then machined with a drill or some other suitable cutting device. Blanks that are molded typically have the cavity already molded in with the use of a core pin.
Some injection molded vials have a rounded top, or viewing window, which provide a magnifying effect to the bubble contained within the cavity of the vial. Perfectly square or rectangular vials do not provide this magnification, and the corners of such vials actually obstruct the view of the bubble, thereby limiting the range of vantage points that may be used to read the vial. Conventional vials with rounded tops have square ends to facilitate assembly to create the level, but these square ends also obstruct the view of the bubble from certain vantage points.
For improved sensitivity of the level, the cavity within a conventional vial is shaped as a barrel rather than a cylinder. However, combining the advantages of the rounded top with the barrel-shaped cavity has led to vials with decreased accuracy. This is due to the injection molding process and the cooling of the blank. Specifically, because molding the blank with a uniform curved outer surface and a barrel shaped inner surface creates a blank with a non-uniform thickness, i.e., the wall at the longitudinal center of the blank is thinner than the wall near the end of the blank, the cooling rate of the material varies with location. The center of the blank will cool more quickly than the ends of the blank. These differences in cooling rates may have a detrimental effect on the dimensional stability of the blank, which may lead to vial inaccuracy.
It is desirable to manufacture a vial that provides magnification of the bubble from a wider range of vantage points, yet has improved accuracy over the conventional vials.